In the oil and gas industry, hydrocarbons are produced from underground formations. In some hydrocarbon-bearing formations, such as sandstone formations, solids may be produced with the hydrocarbons. Production of solids with hydrocarbons is undesirable for many reasons. Fluids containing solids generally are much more erosive, and may damage metallic conduits and pipe in the wellbore and in the surface oil and gas processing equipment. Excess production of solids may plug or block the wellbore, or inhibit flow of fluids through processing equipment. When this occurs, it may require costly wellbore or surface facility cleanout operations before hydrocarbon production may resume.
It is known that solids production varies considerably in different subterranean formations. Solids generally consist of sand (quartz) particles but may also contain other natural or deposited materials such as clays, silts, salts, feldspars, and the like. When completing a well, it is desirable to determine if the well is likely to produce solids with the hydrocarbons. If solids production is likely, then sand or solids production control measures may need to be implemented. Such solids production inhibition methods may include, for example, fracturing and packing the fractured reservoir with sand, gravel or proppant to inhibit further solids production. It may be desirable to install chemical inhibition, consolidation or mechanical screen assemblies in the wellbore. There are many different techniques and equipment available to inhibit solids production. However, solids production control methods must be designed and appropriate for a given wellbore, and the appropriate method may depend upon the depth, pressure, temperature, and other conditions of hydrocarbon production. The implementation of solids production control techniques and installation of solids control apparatus is generally time consuming and costly, as is the addition of surface solids handling and treatment equipment. Further, the requirement to install such equipment reduces the commercial viability of many projects.
The pressure differential between the wellbore and the subterranean formation is an important factor in determining how much solids will be produced. It is desirable, for a given wellbore, to understand the downhole conditions at which the onset of solids production will occur and the volume of solids that can be expected to be produced. By understanding solids production characteristics of a wellbore, it is possible to tailor a solids production control strategy that is likely to prove successful for the least amount of effort and cost.
Solid particles are generally denser than fluids in water and hydrocarbon wellbores. During well tests and in production mode, wellbore fluids need to travel faster than a specific rate to lift solid particles to the surface. Once fluid production is stopped in a typical well test, the solids in the produced fluid settle in the wellbore. Heavier solid particles will settle faster than lighter particles and therefore require a higher fluid velocity to lift them to the surface. Settling of solids in the wellbore presents operational problems, including for example the risk of a stuck drill pipe in subsequent operations. Solids settling velocities also mean that surface samples are an unreliable measure of the total produced solids.
This invention is directed to apparatus and methods for determining or measuring solids production characteristics for a subterranean formation penetrated by a wellbore, while avoiding some of the problems inherent in capturing the solids at surface.